1. Field of the Invention
This invention relates to a process for manufacturing a plasma display panel, and, particularly, to a process for manufacturing a plasma display panel including a novel step of forming a dielectric layer on a glass substrate.
2. Description of the Background Art
A plasma display in the form of a plate-type fluorescent display has attracted considerable attention in recent years. FIG. 1 is a typical view showing a configuration in section of an A.C. type plasma display panel (hereinafter called "PDP"). In this figure, the symbols 1 and 2 represent glass substrates opposedly positioned and the symbol 3 represents a partition wall. A combination of the glass 1, the glass 2, and the partition wall 3 forms divisional cells. The symbols 4, 5, and 6 represent a bus electrode secured to the glass substrate 1, an address electrode secured to the glass substrate 2, and a fluorescent material supported in the cell respectively. The symbol 7 represents a dielectric layer formed on the surface of the glass substrate 1 so as to cover the bus electrode 4. The symbol 8 represents a protective layer made, for example, of magnesium oxide. The dielectric layer 7 is formed of a sintered glass material with a film thickness, for example, of 20 to 50 .mu.m.
In order to form the dielectric layer 7, there is a known process in which a paste composition containing glass powder is prepared and applied to the surface of the glass substrate 1 by screen printing, followed by drying to form a coating material layer which is then burned to remove organic substances thereby baking the glass powder.
In this case, the thickness of the coating material layer is required to be 1.3 to 1.5 times that of the dielectric layer 7 to be formed in consideration of loss in film thickness associated with the removal of organic materials in the baking step. For example, in order for the thickness of the dielectric layer 7 to be 20 to 50 .mu.m, the thickness of the coating material layer must be designed to be about 30 to 70 .mu.m.
On the other hand, if the paste composition containing the above glass powder is applied by screen printing, a film thickness formed by one application is about 15 to 25 .mu.m. This requires plural repetitions (for example, two to five times) of application of the paste composition to prepare a coating material layer with the desired thickness.
The problems to be solved by the invention, especially relating to the screen printing method, are as follows:
(1) Operation of plurally repeated applications of a paste composition (multiple printing) is complicated and is inferior in workability. It is also necessary to confirm the dispersion condition of the components for each application of the paste composition. Redispersion treatment is required when an inferior dispersion, e.g. deposition of glass powder, occurs. Therefore, the conventional method in which a dielectric layer is formed through such a complicated application step has a problem in view of efficiency of producing a PDP. This problem is more significant as the display panel increases in size.
(2) In the case of forming the coating material layer by multiple printing utilizing a screen printing method, the film thickness of a dielectric layer formed by baking the coating material layer is not uniform. The tolerance, for example, within .+-.5% cannot be achieved using this method. This is because it is difficult to uniformly apply the paste composition to the surface of the glass substrate by multiple printing utilizing a screen printing method. The dispersion in the film thickness of the dielectric layer is greater with increased area of application (panel size) and with the number of applications. The dispersion in the film thickness causes dispersion in dielectric properties in the surface of a panel material (the glass substrate provided with the dielectric layer) prepared in the application step using multiple printing. This dispersion in dielectric properties causes display defects (uneven luminance) in the PDP.
(3) In the screen printing method, a small amount of air is trapped in the paste composition passing through a screen and there are cases where this air remains as air bubbles in the coating material layer. When the coating material layer containing an air bubble is baked, pinholes or cracks are produced in the formed dielectric layer. In addition, the (n)th coating tends to be damaged by being squeezed in the step of forming the (n+1)th coating. This causes cracks to occur in the dielectric layer. The insulating properties of the dielectric layer are damaged by the pinholes or cracks whereby the dielectric layer exhibits dielectric properties lower than expected.
(4) In the screen printing method, there are cases where the shape of a screen print mesh is transferred to the surface of the coating material layer. A dielectric layer formed by baking such a coating material layer has a deteriorated surface smoothness.
The present invention has been developed in view of this situation and has an object of providing a process for manufacturing a PDP comprising a novel forming step in which a very thick dielectric layer can be formed in an efficient manner.
Another object of the present invention is to provide a process for manufacturing a PDP comprising a novel forming step in which a dielectric layer required for a large panel can be efficiently formed.
Yet another object of the present invention is to provide a process for manufacturing a PDP comprising a dielectric layer with a highly uniform film thickness.
A further object of the present invention is to provide a process for manufacturing a PDP comprising a reliable dielectric layer having no defects, including pinholes or cracks.
A still further object of the present invention is to provide a process for manufacturing a PDP comprising a dielectric layer possessing excellent surface smoothness.